One example of a vascular implant is described in detail in International Patent Publication No. WO 2004/103 215 A1, in particular, in regard to the fundamental areas of application of such stents and the special problems upon use of materials having a low ductile yield and also lower strengths, such as magnesium alloys.
In the embodiment which may be inferred from this publication, the stent is implemented by a main body circumscribed by a cylindrical shape and radially expandable from a contracted starting position into a dilated support position which, on one hand, comprises multiple support segments running around the circumference and arrayed in the axial direction on one another. The support segments are each formed by a strut which is meandering in coarse structure in its contracted starting position having alternating opposing meandering curves made of flexible material. On the other hand, the main body has axial connectors running in the axial-parallel direction which connect the support segments between zenith points of at least a part of the meandering curves.
The above-mentioned magnesium alloys as the material for producing stents have significantly lower strength values than typical construction materials for balloon-expandable stents, such as medical steel having the material identifications 316L, MP35N or L 605. These lower strength values cause problems in the practical application of the stents. It is thus necessary for the stent placement to mount the stent on a balloon catheter. For this purpose, the stent, which is structured from a sleeve material by laser cutting, for example, is crimped onto the balloon catheter in its contracted starting position. The stent is also guided on the catheter system through curved areas of the insertion or blood vessel system in this state during the implantation. Individual struts of the stent may open in the corresponding passages, by which the retention forces of the stent on the catheter are reduced. This causes a significant risk of loss of the stent.
Especially endangered areas of the stent are the terminal strut elements having their meandering curves. In addition, the danger arises due to projecting edge segments, the so-called “flaring,” that, in addition to the mechanical irritation of the internal vascular wall upon passage of the stenosis or the retraction into the insertion catheter, unintended stripping of the stent from the balloon catheter will occur.